Thanks again Pete. It took a bit to figure out the menu structure as I am not used to it. (I once used several Nikon film cameras but that's no help here!)I like this approach because it's easy enough to switch back to unlocked, and locked makes sense in most landscape situations - the ones I bought the camera for. Generally I want to maximize dof without running into diffraction softness (somewhere around f/13 it seems so far), and therefore there is seldom a need to change aperture. At least at the times when there is no need - most of the time in good enough light that we don't have to start thinking of the exposure variables as we can stop down, keep ISO low and still get a fast shutter speed when hand holding (I use the one second delay) - it can be easy to forget about aperture as it isn't meant to change. Hope this makes sense. Anyway those are the times it will be good to lock the aperture.